Spectrophotometry has, of course, long been used as a valuable investigative tool in various scientific fields, particularly biological and medical research, and various applications of the underlying principles utilizing selected wavelengths of light in the near infrared range (often referred to as N.I.R. spectrophotometry) have for quite some time been utilized for certain in vivo procedures and/or investigation on human beings. For example, a frequently-encountered such device is the pulse oximeter conventionally used in hospitals and other medical facilities to provide a direct indication of arterial oxygen saturation by means of a clip or the like which fastens to an appendage such as the ear or finger of the patient. As has been noted by a small but growing field of investigators, the potentially useful applications of N.I.R. in vivo spectrophotometry are considerably broader and more diverse than this, however, due to the interesting and useful characteristic of N.I.R. wavelengths in being able to pass through ("transmiss") biological substance such as human skin, bone, and tissue for at least a length of several centimeters, and a useful brief description and commentary as to this is set forth in the above-referenced prior applications and/or patents attributable in at least part to the present inventor (see for example U.S. Pat. No. 4,570,638), as well as in the various references of record therein. In the latter regard, particular reference is made to the patents issued to Jobsis et al, e.g. U.S. Pat. Nos. 4,281,645, 4,223,680 and 4,321,930.
While previous developments in the general field of N.I.R. in vivo spectrophotometry, as noted above, have no doubt provided interesting and at least potentially useful insights and information heretofore, many important further developments and applications no doubt remain to be made, and certain of these are likely to be of considerable importance to medical practitioners. For example, accurate, meaningful, non-intrusive monitoring of brain status and viability is a most important need which prior technology has not sufficiently satisfied. As is well known and widely appreciated, the brain is a delicate and easily-damaged portion of human anatomy, while at the same time being the epicenter of neurological and physiological function. Brain damage through injury or cerebral vascular disease is responsible for numerous deaths and serious illnesses each year, involving on the order of at least 100,000 surgical procedures annually in recent years. Brain vitality is primarily a function of oxidative metabolism, and the predominant cause of neurological dysfunction and malfunction relates to the lack of sufficient brain oxidation, typically as a result of obstruction or otherwise insufficient arterial blood flow to the brain. Of course, this can occur even during surgery, and it has been estimated that at least 2,000 patients die each year in the United States alone due to anesthetic accidents, while numerous other such incidents result in brain damage of some degree; at the same time, certain major and complex surgical procedures, particularly of a neurological, cardiac or vascular nature, may require induced low blood flow or pressure conditions, which inevitably involves the potential of insufficient oxygen delivery to the brain. At the same time, the brain is the human organ which is most intolerant of oxygen deprivation, and brain cells will die within a few minutes if not sufficiently oxygenated. Moreover, such cells are not replaced, and thus involve irreversible brain damage which may potentially result in paralysis, disability, or even death.
Accordingly, the availability of immediate and accurate information concerning the state of brain oxygen saturation is of critical importance to anesthesiologists and surgeons, as well as other involved medical practitioners, particularly since the patients involved are typically in an unconscious state and thus unable to provide information by ordinary physical response. Up until the present time, however, the instrumentalities available for use, including such things as electroencephalograph ("EEG"), arterial pulse oximeter and blood pressure monitors, etc., and even invasive catheter monitoring of blood oxygen content, acidity, etc. by penetration of the jugular bulb (jugular vein) do not provide accurate, ongoing, timely (instantaneous) information as to cerebral (brain) blood oxygenation state, particularly since the brain blood supply is extensive, diffuse, pervasive, and largely venous in nature rather then arterial. Of course, it is also thus devoid of conventional pulsative characteristics essential to the operation of conventional oximeters.
Accordingly, such devices are not appropriate for cerebral usage, and of course they are typically made to be applied only to peripheral tissue or appendages in any event, i.e., a finger or an ear lobe, and are not utilized in conjunction with venous blood. Of course, jugular bulb catheters are highly invasive and relatively traumatic; at the same time, they merely provide blood samples which are removed and analyzed in another location, at a subsequent point in time, and thus only address the state of venous blood after it has left the brain.